Human immunodeficiency virus type 1 integrase: arrangement of protein domains in active cDNA complexes

Early steps of retroviral replication involve reverse transcription of the viral RNA genome and integration of the resulting cDNA copy into a chromoso me of the host cell. The viral-encoded integrase protein carries out the in itial DNA breaking and joining reactions that mediate integration. The orga nization of the active integrase-DNA complex is unknown, though integrase i s known to act as a multimer, and high resolution structures of the isolate d integrase domains have been determined. Here we use site-specific cross-l inking based on disulfide bond formation to map integrase-DNA contacts in a ctive complexes. We establish that the DNA-binding C-terminal domain of one integrase monomer acts with the central catalytic domain from another mono mer at each viral cDNA end. These data allow detailed modeling of an integr ase tetramer in which pairs of trans interactions link integrase dimers bou nd to substrate DNA. We also detected a conformational change in integrase- DNA complexes accompanying cleavage of the viral cDNA terminus.